1. Field of the Invention
The present invention relates to improvements of a chain block that winds up, unwinds, or pulls a load chain holding a load in response to a manual operation of a hand chain.
2. Description of the Related Art
Chain blocks typically raise and lower a load chain in a winding operation in response to the manual operation of a hand chain. FIG. 4 illustrates a typical structure of a chain block. A load sheave 50 is rotatably supported by bearings 52 at a main frame 51. A load chain (not shown) is wound up on the load sheave 50 to raise a load. A hand wheel 53 is rotatably supported on one side of the main frame 51 shown in the left-hand of FIG. 4. The hand wheel 53 transfers a force required to perform the winding operation to the load sheave 50. A hand chain (not shown) is wrapped around the hand wheel 53. By manually operating the hand chain, the force applied to the hand chain is transferred to the load sheave 50 via a transfer mechanism to be discussed later. The winding operation is performed to raise and lower the load. The transfer mechanism includes a pinion shaft 55, a reduction gear 56, and a main shaft gear 57. One end of the pinion shaft 55 is inserted into the center hole of the load sheave 50 in a manner such that the load sheave 50 is rotatable on the pinion shaft 55, and the other end of the pinion shaft 55 includes a spindle gear 54. The reduction gear 56, arranged on the side of the main frame 51 opposite from the hand wheel 53, includes a large-diameter gear 56a and a small-diameter gear 56b in a unitary body. The large-diameter gear 56a is in meshing engagement with the spindle gear 54. The small-diameter gear 56b of the reduction gear 56 is in meshing engagement with the main shaft gear 57. To reliably transfer the torque of the pinion shaft 55 to the main shaft gear 57, two reduction gears 56 are arranged on both sides of the center axis of the pinion shaft 55 (i.e., one in front of and the other behind the plane of the page of FIG. 4). Alternatively, the two reduction gears 56 may be arranged, one above and the other below the center axis of the pinion shaft 55. The main shaft gear 57 is connected to the load sheave 50 by lock pins 58 so that the main shaft gear 57 integrally rotates with the load sheave 50. A ratchet gear 60 is arranged between the hand wheel 53 and the load sheave 50. The ratchet gear 60 is engaged with a ratchet pawl 59 to prevent the hand wheel 53 from rotating in a reverse direction. A fixed friction plate 62 is arranged next to the ratchet gear 60 so that the fixed friction plate 62 is frictionally engaged with a brake lining 61 on the ratchet gear 60. Lock pins 63 connect the fixed friction plate 62 to the pinion shaft 55 so that the fixed friction plate 62 is restricted in rotation and in axial movement.
When the hand wheel 53 is rotated by manually operating the hand chain in the chain block thus constructed, the force applied to the hand chain is transferred to the fixed friction plate 62 and the pinion shaft 55 via the brake lining 61 so that the fixed friction plate 62 and the pinion shaft 55 integrally rotate. The torque of the pinion shaft 55 is further transferred to the main shaft gear 57 via the spindle gear 54 and the reduction gear 56. As a result, the load sheave 50 rotates, thereby performing the winding operation on the load chain.
Japanese Unexamined Patent Application Publications Nos. 6-115883 and 7-309591 disclose techniques that allow a load sheave corresponding to a load chain in a chain-lever hoist to freely rotate with no load applied.
In this type of the chain block, the load chain is preferably free to move with no load applied. The chain block is typically used at an elevated location, and cannot be directly operated. The chain block has no mechanism to allow free rotation. To perform the winding operation of the load chain with no load applied, the hand chain needs to be repeatedly moved with the reduction gear applied. A lot of energy is required to perform the winding job.